Electromagnetically controlled fluid friction coupling

ABSTRACT

The invention relates to a fluid friction coupling comprising a drive shaft ( 2 ) and a drive disk ( 4 ) which is rotationally fixed thereon, in addition to a drive housing ( 5 ) which is rotationally arranged on the drive shaft ( 2 ). The drive disk forms a working area ( 7 ) and a storage area ( 9 ) enabling a fluidic connection for a viscous medium via a feed hole ( 11 ) and a return channel ( 8 ). The feed hole ( 11 ) is controlled by a valve lever ( 12 ) with an anchor plate ( 14 ) by means of an electromagnet ( 19 ) arranged on the near side of the coupling. According to the invention, the valve lever ( 12 ) is arranged between the drive disk ( 4 ) and the electromagnet ( 19 ) and the anchor plate ( 14 ) is arranged in the magnetic flow area of the electromagnet ( 19, 20 ).

The invention relates to a fluid friction coupling according to the preamble to claim 1. Such a coupling has been disclosed by DE-A 199 25 132.

In this known fluid friction coupling a valve lever, which controls the circulation of a viscous medium through the coupling, is controlled by an electromagnet, which is rotatably arranged on the rear side of the coupling, that is to say to the side of the drive engine. The valve lever, on the other hand, is situated on the front of the coupling, that is to say on the side remote from the engine and the electromagnet in front of the drive disk (primary disk) of the coupling. The magnetic flux from the coil of the electromagnet to the valve lever, which has an armature base plate, is by way of specially designed conducting rings, which are composed of magnetically conductive material and are partially cast into the body of the coupling. A disadvantage with this magnetic flux conduction is that a relatively large number of parts is needed for the magnetic flux conduction and that the coupling has a relatively large overall depth.

The object of the present invention is to reduce the overall depth of the aforementioned fluid friction coupling and to improve the magnetic flux, in order thereby to reduce the energy expenditure for the coil of the electromagnet.

This object is achieved in the aforementioned coupling by the features of the characterizing part of claim 1. Arranging the valve lever between drive disk and electromagnetic coil shortens the path of the magnetic flux between coil and armature base plate of the valve lever, that is to say the magnetization losses and the energy expenditure for the coil are reduced. At the same time the overall axial depth of the coupling is shortened.

Although DE-A 32 43 967 has already disclosed a fluid friction coupling with electromagnetic control of a valve lever, which is arranged between primary disk and electromagnetic coil, this coupling exhibits considerable differences with regard to the arrangement of the electromagnet and the magnetic flux conduction via so-called pole rings, as well as the position of reservoir chamber and working chamber, the differences resulting, among other things, in a relatively large overall depth.

According to one advantageous further embodiment of the invention the reservoir chamber for holding the viscous fluid is arranged on the front of the drive disk, whilst an intermediate chamber which has a fluid connection to the working chamber is situated on the rear side. This design means that the viscous medium is fed radially inwards to radially outwards to the working chamber, that is to say under the effect of centrifugal force and on the rear side of the drive disk. This ensures a proper supply of viscous fluid to the working chamber and reliable activation of the coupling.

According to a further advantageous development of the invention the valve lever with its armature base plate is fixed to the drive disk, in which the feed hole is also arranged. This produces a compact construction.

Further advantageous developments of the invention are set forth in the dependent claims.

An example of an embodiment of the invention is shown in the drawing and is described in more detail below. In the drawing

FIG. 1 shows section through a fluid friction coupling.

FIG. 1 (the single FIGURE) shows a sectional representation of a fluid friction coupling 1. The coupling 1 comprises a drive part and an output part, the drive part being formed by a drive shaft designed as hollow shaft 2, a hub 3 fixed thereto and a drive disk 4 fixed on the hub 3. The output part of the coupling 1 comprises a two-part coupling housing 5, which is formed from a body 5 a and a cover 5 b. The body 5 a is rotatably supported on the hollow shaft 2 by means of a deep-groove ball bearing 6. The coupling housing 5 together with the drive disk 4 forms a working chamber or shear chamber 7 which, as is known in the art, is formed by annular ribs 7 a on the output side 5 b and annular ribs 7 b on the drive side 4. The annular ribs 7 a and 7 b form a meander-shaped labyrinth gap 7 c, containing shear fluid, that is to say a viscous medium. From the working chamber 7 a return duct 8 in the coupling cover 5 b leads into a reservoir chamber 9, which is formed by the drive disk 4 on the one hand, and on the other by an intermediate disk 10 affixed thereto. The reservoir chamber 9 therefore rotates with the drive disk 4. In the drive disk 4, radially inside the labyrinth gap 7 c, is a feed hole 11, which leads from the front of the drive disk 4 to the rear side. A valve lever 12, which with its (in the drawing) lower end 12 a is fixed to the drive disk 4 by means of rivet 13, is arranged on the rear side of the drive disk 4. An armature base plate 14 is fixed on the valve lever 12. The valve lever 12 is of flexible design and under its own internal stress, especially at its (in the drawing) upper end 12 b, bears on the drive disk 4 in the area of the feed hole 11, and closes the latter. Between the rear side of the drive disk 4 and the body 5 a is an intermediate chamber 15, which leads via duct 16 running radially in the drive disk 4 into the working chamber 7. The drive disk 4 has a plurality of ducts 16 evenly distributed over the circumference, which are not discernible from this sectional representation.

A magnet assembly 19 is fixedly supported on the hollow shaft 2 immediately next to the body 5 a by means of a deep-groove ball bearing 18 and is axially fixed on the hollow shaft 2 by way of a flange 17. The magnet assembly 19 comprises a coil 20, which is enclosed by a radially outer magnet casing 21 and a radially inner magnet casing 22. Current is fed to the coil 20 via a connection part 23 formed in plastics. The overall magnet assembly 19 with connection part 23 is fixedly supported by way of a schematically represented torsional brace 24, for example on the engine housing 25. At the radial height of the outer magnet casing 21 a steel insert 26 is cast in the body 5 a, which is made of an aluminum alloy, said insert exercising the function of a conducting ring for the magnetic flux. The end 26 a of the steel insert 26 emerging from the body 5 a into the intermediate chamber 15 is situated directly opposite the armature base plate 14 of the valve lever 12 and between them is a gap 27.

The coupling 1 is connected to the drive shaft (not shown in the drawing) of an engine or a coolant pump shaft of an internal combustion engine by means of a fixing bolt (likewise not shown) inserted through the hollow shaft 2, as is described and represented in more detail, for example, in DE-A 31 48 872 filed by the present applicant. Fixed to the housing 5 b of the coupling 1 is a fan 28 (partially shown), which serves to deliver ambient air through a radiator (not shown) for the coolant circuit of an internal combustion engine of a motor vehicle.

When the hollow shaft 2 and hence the drive disk 4 are being driven, the viscous fluid, a silicone oil, present in the reservoir chamber 9 is forced outwards by centrifugal force and in the reservoir chamber 9 forms a fluid ring, which when the feed hole 11 is closed by the valve lever 12 is retained in the reservoir chamber 9. That is to say no silicone oil flows into the working chamber 7. Instead, the silicone oil present in the working chamber 7 is pumped out by a choke element 29 and is delivered by way of the return duct 8 into the reservoir chamber 9. The coupling thereby switches off, because there is no longer any silicone oil in the labyrinth gap 7 c and hence no further torque is transmitted. Should the coupling be switched on in order to drive the fan 28, the magnetic coil 20 is energized, so that a magnetic flux is formed via the steel insert 26 towards the armature base plate 14 and pulls this to the right. The valve lever 12 is thereby lifted off from the feed hole 11, and the viscous medium under the action of the centrifugal force now flows via the intermediate chamber 15 and the duct 16 into the working chamber 7, so that the coupling is switched on. When the armature base plate 4 is attracted by the magnetic coil 20, it must be ensured that the end 26 a of the steel insert 26 and the armature base plate 14 do not come into contact, since the two parts are rotating at different speeds. This is ensured by means of a stop 30 on the drive disk 4 or on the coupling hub 3.

When the coil 20 is energized, a closed ring forms for the magnetic flux, which starting at the magnetic coil runs via the outer magnet casing 21 and the steel insert 26 into the armature base plate 14 and thence via a partial area of the hub 3 and the hollow shaft 2 back into the inner magnet casing 22. In this way a short and effective magnetic flux conduction is achieved, so that a small coil is sufficient to actuate the valve lever with a low energy expenditure.

List of Reference Numerals

-   1 Fluid friction coupling -   2 Hollow shaft -   3 Hub -   4 Drive disk -   5 Output housing -   5 a Body -   5 b Cover -   6 Deep-groove ball bearing -   7 Working chamber -   7 a Annular rib, output side -   7 b Annular rib, drive side -   7 c Labyrinth gap -   8 Return duct -   9 Reservoir chamber -   10 Intermediate disk -   11 Feed hole -   12 Valve lever -   13 Rivet -   14 Armature base plate -   15 Intermediate chamber -   16 Feed duct -   17 Flange on hollow shaft -   18 Deep-groove ball bearing -   19 Electromagnet assembly -   20 Coil -   21 Outer magnet casing -   22 Inner magnet casing -   23 Connection part -   24 Torqsional brace -   25 Engine block -   26 Steel insert -   26 a End of steel insert -   27 Gap -   28 Fan -   29 Choke element -   30 Stop 

1. A fluid friction coupling, comprising a drive shaft (2) and a drive disk (4) which is rotationally fixed thereon, and an output housing (5), which is rotatably supported on the drive shaft (2) and with the drive disk (4) forms a working chamber (7) and a reservoir chamber (9), which between them have a fluid connection for a viscous medium by way of a feed hole (11) and a return duct (8), the feed hole (11) being controllable via a valve lever (12) with armature base plate (14) by means of an electromagnet (19) arranged on the rear side of the coupling, characterized in that the valve lever (12) is arranged between the drive disk (4) and the electromagnet (19) and the armature base plate (14) is arranged in the magnetic flux area of the electromagnet (19, 20).
 2. The fluid friction coupling as claimed in claim 1, characterized in that the reservoir chamber (9) for holding the fluid flowing back from the working chamber (7) is arranged on the front of the drive disk (4), that the feed hole (11) is arranged in the drive disk (4) and that an intermediate chamber (15), which has a fluid connection to the working chamber (7), is arranged on the rear side of the drive disk (4).
 3. The fluid friction coupling as claimed in claim 2, characterized in that the intermediate chamber (15) is connected by radial feed ducts (16) to the working chamber (7).
 4. The fluid friction coupling as claimed in claim 1, characterized in that the valve lever (12) is fixed to the drive disk (4).
 5. The fluid friction coupling as claimed in claim 4, characterized in that the valve lever (12) is fixed, by its end (12 a) diametrically opposed to the feed hole (11), to the drive disk (4) and under spring tension bears on the drive disk (4) in the area of the feed hole (11).
 6. The fluid friction coupling as claimed in claim 1, characterized in that the drive shaft is designed as hollow shaft (2) to accommodate a central fixing bolt.
 7. The fluid friction coupling as claimed in claim 1, characterized in that the output housing (5) has an aluminum body (5 a) with cast-in steel insert (26, 26 a) in the area of the magnetic flux of the electromagnet (20).
 8. The fluid friction coupling as claimed in claim 1, characterized in that the magnetic flux forms a substantially closed ring incorporating an outer magnet casing 21 enclosing the electromagnet (20), the steel insert (26), the armature base plate (14), a partial area of a coupling hub (3), the hollow shaft (2) and an inner magnet casing (22). 